On September 23rd 1999, the Mars Climate Orbiter spacecraft vanished.
Gone for ever.
The management team at NASA promptly set out on a lengthy investigation to answer the following question: How does a $125 million spacecraft simply disappear?
After months of work, the report eventually revealed the root cause to be a failure to convert from imperial units (pounds) to metric units (newtons).
The engineers at the Orbiter’s manufacturer Lockheed Martin typically use imperial units in their measurements. The opposite was true for NASA who use the metric system.
As a result, the software of the craft’s control thrusters measured force in pounds but a separate piece of software assumed the data was in newtons.
This small error resulted in it flying more than 50 miles off course.
Eventually, it flew too close to Mars and disappeared into the Martian atmosphere.
A similar and equally simple miscalculation error occurred on an Air Canada flight in the 1980s. Fortunately, for the passengers on board, the pilot was also an experienced glider and managed to fly the aircraft (without fuel) to safety.
The above expensive mistakes illustrate how small errors in complex systems can have a catastrophic impact and highlights the importance of checklists as an effective and often lifesaving tool.